Transformers containing nonflammable dielectric fluids which contain polychlorinated biphenyls (PCBs) should be drained and refilled with high flashpoint dielectrics that do not contain PCBs. Methods currently proposed for removing the PCB dielectric and replacing the PCB dielectric with non PCB dielectrics do not appear to be capable of preventing PCB contamination of the non PCB replacement dielectric. One such method suggests removing the PCB dielectric material and refilling the transformer with biodegradable high flashpoint dielectric liquid. A connection is made between the transformer and a container full of a filter material and the transformer liquid is continually transported through the filter material during transformer operation. Once the transformer dielectric reaches a low level of PCB contamination, the filter is removed and the transformer is allowed to operate as a non PCB transformer. The material comprising the filter is proprietary to the manufacturer, and is not generally known. It is believed, however, to be specific to the biodegradable dielectric fluid used as the PCB replacement dielectric and it is not known whether the same filter material would work with a high flashpoint silicone dielectric fluid.
The purpose of this invention is to describe methods and materials used for removing residual PCBs from transformers that have been drained and retrofilled with silicone dielectric fluid.